Molecular Constants. 335 
was presented to zinc, the mercury would penetrate the zinc 
and carry the alkaline metal with it. Accordingly the above 
potassium amalgam was introduced into a hollow cylinder of 
cast zinc, 17 millim. internal, and 21 millim. external dia- 
meter (thickness 2 millim.), 45 millim. external height, 35 
millim. internal height (10 millim. thickness of bottom). The 
amalgam was scraped upon the zinc so as to ensuregContact, and 
then covered with petroleum. The zinc cylinder was thereupon 
corked up and covered with paraffin. It was placed in a 
beaker of distilled water and covered with a tube of water 
according to fig. 7. After two months' standing at a uni- 
form temperature of about 15°, scarcely a pin's-heacl volume 
of gas had collected in the top of the tube. Abundance 
of the semiflocculent fine oxy hydro- carbonate had coUected 
on the zinc and at the bottom of the beaker. That part 
on the zinc was rubbed off the zinc with an ivory blade, 
and, together with the sediment in the beaker, dissolved in 
hydrochloric acid overneutralized with ammonia and sulphide 
of ammonium. After separation of the Zn, no trace of K 
could be found. No potassium had found its way through the 
zinc. Perhaps a more remarkable fact still is this, that on 
scraping about a gram of the solid metal from the outside of 
the zinc cylinder, not a trace of mercury could be found in 
it. Not only, therefore, did the alkaline metal fail to follow 
the mercury into the zinc, but it prevented the mercury from 
entering the zinc. Compare this with § 32, where the cylinder 
of zinc is literally " slaked " by the mercury. 
§ 31. Cylinders of zinc, lead, and tin were cast, an inch and a 
quarter long and -J inch in diameter. These were floated on the 
mercury contained in the tubes described in § 28. The quantity 
of the mercury in each tube was such that it stood at the same 
height, reckoning from the bottom of each cylinder. The 
burettes had been previously lashed to massive stands, cork 
buffers being interposed between the tubes and the stands. 
The three were placed side by side on a slab let into the wall, 
and were protected as much as possible by cloths from sudden 
changes of temperature. The mean temperature was 15° C. 
The experiments lasted a month, and the extreme range of 
temperature was from 13° C. to 17°*5 C. 
At the end of the month (31 days) the mercury was run 
off from the bottom very slowly and discontinuously into the 
paraffin vessel described in § 28 ; so that, with the exception 
of the top quantities, the volumes of the successive portions 
were very nearly the same. With regard to the top quantities, 
it is clear that, since the metals float at different depths in the 
mercury, the surfaces of contact are not the same in the 
